The crash of a Malaysia Airlines jetliner in Ukraine came just months after the disappearance of another of the carrier's planes, a second serious blow for a company already on a shaky financial and operational footing.

Airline executives had little information to offer about Flight 17 late Thursday in Kuala Lumpur. The Boeing 777 had at least 283 passengers and 15 crew members on board. But the crash seemed certain to subject the...